Living Carbocationic Sequential Block Copolymerization of Isobutylene with .alpha.-Methylstyrene

Abstract

The polymerization of α-methylstyrene (αMeSt) was investigated using the 2-chloro-2,4,4-trimethylpentane (TMPClTiCl 4 /methyl chloride :hexane (40 :60, v :v)/-80 °C system as a model to determine the efficiency of crossover from living polyisobutylene (PIB) to αMeSt. Low initiator efficiencies and broad molecular weight distributions were obtained. Living polymerization of αMeSt was achieved by first converting TMPCl to the corresponding diphenylalkylcarbenium ion by capping with 1,1-diphenylethylene (DPE), followed by the addition of titanium(IV) alkoxide to decrease the Lewis acidity. The initiator efficiencies, however, were lower than 100%. Living polymerization with ∼100% initiator efficiency was achieved by SnBr 4 as coinitiator. First, TMPCl is transformed to the corresponding diphenylalkylcarbenium ion by capping with 1,1-diphenylethylene. Subsequently, titanium(IV) isopropoxide is introduced to deactivate TiCl 4 , followed by the addition SnBr 4 and αMeSt. The success of the method was demonstrated by the synthesis of PIB-poly(α-methylstyrene) diblock copolymers without homopolymer contaminants.